1. Field
Embodiments of the present invention generally relate to method and apparatus for processing a semiconductor substrate. More particularly, embodiments of the present invention provide method and apparatus for processing a semiconductor substrate with improved uniformity.
2. Description of the Related Art
When processing substrates in a plasma environment, the uniformity of the plasma will affect the uniformity of processing. For example, in an etching process, more material is likely to be removed or etched from the substrate near the center of the substrate as compared to the edge of the substrate when plasma of the processing gases is greater in the area of the chamber corresponding to the center of the substrate. Similarly, if the plasma is greater in the area of the chamber corresponding to the edge of the substrate, more material may be removed or etched from the substrate at the edge of the substrate compared to the center of the substrate
Non-uniformity in plasma processes can significantly decrease device performance and lead to waste because the deposited layer or etched portion is not consistent across the substrate.
Excellent process uniformity has become increasingly important as semiconductor devices become continuously more complex. Uniformity is important in both the feature-scale (<1 micron) and the wafer-scale (300 mm). Non-uniformities arise from a variety of reasons, for example variation of concentration of different ingredients of a processing gas, such as etching and passivating species, ion bombardment flux and energy, and temperature within the feature profile and across the wafer.
One of the non-uniformities observed is CD (critical dimension) bias edge roll-off. CD bias refers to the difference between the critical dimension of a feature before and after processing. CD bias edge roll-off refers to decrease of CD bias toward an edge of a substrate compared to CD bias near a central region of the substrate.
FIG. 1 schematically illustrates a CD bias edge roll-off of a hard mask etching process in a gate etching application. FIG. 1 demonstrates a critical dimension from bottom measurement of isolated features across a radius of a substrate after etching. The x-axis of FIG. 1 indicates a distance from the center of the substrate, and the y-axis indicates a critical dimension measurement. The CD bias edge roll-off is obvious from the decrease of the critical dimension measurement from 110 mm to 150 mm, i.e. towards the edge of the substrate. Additionally, FIG. 1 also illustrates non-uniformity near a center of the substrate where the critical dimension measurements are lower than a middle section of the substrate.
Traditionally, non-uniformity during etch, such as the CD bias edge roll-off shown in FIG. 1, is controlled by maintaining a temperature gradient across the substrate using heaters in the substrate support. However, in most applications, adjusting the substrate temperature gradient is still an inadequate method to tune the CD bias edge roll-off.
Therefore, there is a need for apparatus and method for processing a semiconductor substrate with reduced CD bias edge roll-off and other non-uniformity.